Heartburn, Indigestion, and Antacids

Hydrochloric acid(HCl), which is necessary for proper digestion of food, is present in the gastric juices of the human stomach. Overeating and emotional factors can cause the stomach to produce too much hydrochloric acid. This leads to hyperacidity, the condition we often call "acid indigestion" or "heartburn". Substances known as antacids provide symptomatic relief from such hyperacidity. An antacid is an over-the-counter drug containing one or more basic substances that are capable of neutralizing the hydrochloric acid in gastric juice.

Alka Seltzer contains sodium bicarbonate, a substance which reacts with acid to produce carbon dioxide gas.

Only a few different neutralizing agents are present in the wide variety of brand-name antacids available.

1.    Slightly soluble hydroxides such as magnesium hydroxide, Mg(OH)2, and aluminium hydroxide, Al(OH)3

2.    Water-soluble sodium bicarbonate,NaHCO3

3.    Very slightly soluble calcium carbonate, CaCO3

4.    Complex hydroxide compounds such as AlMg(OH)5 and NaAl(OH)2CO3

Magnesium hydroxide and aluminium hydroxide react with hydrochloric acid by the following neutralizations:

The reaction involving sodium bicarbonate produces a gas in addition to a salt and water,

In the complex hydroxide AlNa(OH)2CO3, both the hydroxide ion and the bicarbonate ion consume acid.

No antacid formulation is "ideal". Aluminium and calcium preparations tend to cause constipation, whereas magnesium preparations acts as laxatives. (This is one reason for using formulations that contain more than one neutralizing ingredients.) Sodium bicarbonate reacts quickly but has a short relief time (5 minutes) and tends to decrease stomach acidity too much.Calcium carbonate gives a longer relief time (30 minutes) but also tends to decrease stomach acidity too much. (An excessive decrease in stomach acidity causes acid rebound, the body's secretion of more hydrochloric acid.) The following table lists the neutralizing agents present in selected brand-name antacids.

Brand name                     Neutralizing agents

                                                              Alka-Seltzer                     NaHCO3

                                                              Gelusil                             Mg(OH)2, Al(OH)3

                                                              Milk of Magnesia            Mg(OH)2

                                                              Mylanta                           Mg(OH)2, Al(OH)3

(You can find all these brand names in Watson's or other drug stores.)